Process for the production of unsaturated hydrocarbons from liquid hydrocarbons



1961 A. STEINHOFER ETAL 3,005,857

PROCESS FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS FROM LIQUID HYDROCARBONS Filed Sept. 29, 1959 VA POR FIG. I

VAPOR FIG. 2

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INVENTORS. ADOLF STEINHOFER KARL BUSCHMANN LEO UNTERSTENHOEFER BY "1 2m 514 75.;

ATTEY PROCESS FOR THE FROlJUCTION F UNSATU- 1 RATED HYDROCARBONS FROM LIQUID HY- DROCARBONS Adolph Steinhofer, Ludwigshafen (Rhine), Karl Buschmann, Neustadt, Weinstrasse, and Leo Unterstenhoefer, Limhurgerhof, Pfalz, Germany, assignors to Badische Amlin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed Sept. 29, 1959, Ser. No. 843,099 Claims priority, application Germany Sept. 30, 1958 i Claims. (Cl. 260679) This invention relates to a process for the production of unsaturated hydrocarbons by thermal cracking of unsaturated hydrocarbons in hot gases.

It is known to prepare unsaturated hydrocarbons by cracking hydrocarbons in a hot gas atmosphere, possibly with the supply of steam. The substance to be cracked is conveniently introduced into the reaction chamber by atomization by means of nozzles or in vapor form. The heat necessary for the cracking is supplied either by burning part of the initial material or by superheated steam. An intense and thorough mixing of all the components in the reaction chamber is aimed at so that as rapidly as possible a uniform temperature is set up over the whole cross-section and length of the reaction chamber.

This process has the disadvantage that part of the substance to be cracked is cracked at the hot wall of the reaction chamber so that carbon black-and coke are formed which may give rise to disturbances in the reaction chamber and also in the apparatus attached thereto behind the same. This disadvantage is especially evident in the cracking of high boiling hydrocarbons, as for example heavy residue oils, because these are very .difficult to atomize and tend to a high degree to form carbon black and coke.

One object of theinvention is to provide a process for the production of unsaturated hydrocarbons, especially ethylene, propylene and acetylene, by thermal cracking in hot gases, by which the formation of carbonaceous deposits, e.g., carbon black and coke, is avoided.

Another object of'the invention is to provide a method of thermally cracking liquid hydrocarbons by means of hot gases, in which no heat-carrying solids are used.

A further object of the invention is to provide a process of the said kind, in which the liquid hydrocarbons are vaporized inside the reaction chamber rather than prior to their introduction into the same.

We have now found that these and other objects are achieved and the formation of carbon black and coke is avoided by keeping the wall of the reaction chamber colder than the inner free reaction space in which the thermal cracking proceeds. A temperature distribution of this kind is achieved by allowing gases or vapors, especially steam, acting as a propellant, of a temperature which does not cause appreciable cracking, i.e., about 200 to 400 C., advantageously 250 to 350 C., to flow with a high speed of 50 to 300 meters per second, especially 100 to 200 meters per second, tangentially into a cylindrical reaction chamber through which hot gases flow axially as a heat carrier. The substance to be cracked is introduced through one or more tubes near to the wall with a free outlet to the chamber Wall, advantageously tangentially or radially, so that it is spread out by the tangential stream of propellant gas to form a rotating band like a film along the wall of the chamber. The liquid hydrocarbons are thereby vaporized by heat radiation from the core of the chamber and brought by gradual thorough mixing with the hot gases to the temperature necessary for cracking. The average temperature of the reaction mixture on its path through the reaction chamber increases Patented Oct. 24, 1961 continually from the beginning of the reaction chamber to its end. In general, the process is carried out at temperatures between 600 and 1400 C. When using high temperatures, as for example about 900 to 1400" C., and very short residence periods, mainly acetylene is obtained, and at lower temperatures (600 to 900 C.) and longer residence periods, mainly olefines are produced.

Initial materials which may be used in the process according to our invention are hydrocarbons which are liquid under normal conditions. Suitable hydrocarbons include gasolenes, petroleum and petroleum fractions as well as residues from petroleum distillation, such as gasolene having a boiling range fromto 220 C., middle oil fractions boiling between and 350 C., as well as higher-boiling hydrocarbons such as bunker-C oil.

It is possible to add gases to the steam. Such gases include inert gases such as nitrogen or carbon dioxide, combustible gases such as hydrogen and/or carbon monoxide, and also mixtures thereof. The amount of gas used may be, for example, from 10 to 80% by volume with reference to steam. The steam may be usedfin amount of from 0.2 to 1 kg, preferably 0.3 to 0.5 kg, per kilogram of hydrocarbon introduced.

The heat required for the cracking is introduced directly into the reaction zone by means of hot gases. Gases which may serve as heat carriers include inert gases, such as nitrogen or carbon dioxide, and vapors, e.g. steam. It is preferable, however, to produce a hot gas in a combustion chamber arranged before the reaction chamber by burning a fuel, e.g., natural gas, gasolenes, or fuel oil, and to introduce the hot gas directly into the reaction chamber. In order to maintain the heat necessary for the cracking the hot gas should be heated to a temperature of between 800 and 1500 C., preferably between 1000 and 1400 C.

The invention will now be further described in connection with various embodiments of reaction chambers which have proved suitable in practice, but these embodiments are described merely by Way of example. Refer- 'ence will be made to the accompanying drawings in which three embodiments are shown in sectional elevation.

Referring first to FIGURE 1, combustion gas produced in a burner 1 is led through an intermediate member 2, which may have various shapes depending on the liquid hydrocarbon being used and the desired cracked products, into a reaction chamber 3 in axial direction. The intermediate member 2 may, as shown in FIGURE 1, be offset from the reaction chamber 3, or as shown in FIG- URE 2, may pass into the same directly without forming corners. Through an attachment 4, having a tangential rectangular opening into the reaction chamber, the propellant gas flows at a temperature up to about 300 C., and the liquid hydrocarbon freely flowing through a pipe 5 is thereby spread out to a film-like band on the wall of the chamber. The propellant gas, for example steam or another vapor or gas, with which oxygen may also be mixed in order to achieve the desired temperature, advantageously to 200 C., by combustion of part of the combustible fraction, rotates along the wall of the chamber at high speed. In the interior of the chamber, the combustion gas flows in axial direction. By its heat radiation it vaporizes the introduced liquid hydrocarbon and mixes therewith. The cracking of the vapors of the hydrocarbon thereby takes place to form unsaturated hydrocarbons. The propellant gas which cools the wall of the chamber mixes during its path to the end of the chamber with the cracked gases until the intended cracking temperature is achieved through the entire cross-section of the chamber. FIGURES l to 3 give difierent possibilities for the construction of the reactors. According to FIGURE 3, the intermediate member 2 is oflset with respect to the reaction chamber 3. The latter is subdivided into two chambers of which the first is connected to the second by a conical section and the second widens conically toward its end. There are of course other possibilities for the shape of the new reactors. Thus for example intermediate member 2 may also be prolonged by a hollow jet member of refractory material to enhance the heat radiation to the film-like band of liquid hydrocarbon and a part may project into the reaction chamber.

Behind the reaction chamber, the gaseous unsaturated hydrocarbons produced are cooled to such a temperature that after-reactions can no. longer occur. This is effected for example by spraying in Water or by injecting other volatile cooling agents. Since it is preferable to carry out the process under a pressure of 2 or more, e.g. 2 to 50, especially '15 to 30 excess atmospheres, the cooling may also be achieved by partial or complete decompression of the gases.

The following example will further illustrate this invention but the invention is not restricted to this example.

Example For the production of heat for cracking, 18 kilograms per hour of heavy residue oil are burned in a previous burner with the addition of 22.5 kilograms per hour of steam. 17 cubic meters of oxygen per hour being necessary for the purpose. The gas passes into the reaction chamber at a temperature of about 1200 to 1300 C. 31 kilograms per hour of bunker-C oil are introduced into the reaction chamber at the same time. 13.5 kilograms per hour of steam, serving as a propellant, are used for spreading out the oil. The cracking temperature decays from 780 C. to about 550 C. The composition of the cracked gas obtained is as follows:

14.7% by volume of carbon dioxide. 17.4% by volume of olefines.

2.2% by volume of acetylene.

31.6% by volume of hydrogen.

25.7% by volume of carbon monoxide. 0.6% by volume of ethane.

7.8% by volume of methane.

Traces by volume of oxygen and nitrogen.

We claim: 1. A process for the production of unsaturated hydrocarbons selected from the group consisting of ethylene,

propylene and acetylene by thermal cracking of hydrocarbons which are liquid under normal conditions in hot gases at temperatures of from 600 to 1400 C., which comprises introducing a liquid hydrocarbon onto the inner wall of a cylindrical reaction zone, spreading out said liquid hydrocarbon to be cracked to a film-like rotating band on said inner wall of said cylindrical chamber by means of steam introduced tangentially with respect to said inner wall and having a temperature below that which efliects appreciable cracking and at a speed of to 30-0 meters per second, and vaporizing and cracking the liquid hydrocarbons by means of a hot gas which is made to enter the cylindrical zone at a temperature of from 800 to1500" C. and which fiows through said cylindrical zone in axial direction.

2. A process as claimed in claim 1 wherein operation is at a pressure of more than 2 excess atmospheres.

3. A process as claimed in claim 1 wherein the cracking gas obtained is rapidly cooled by spraying in water to such a low temperature that side reactions are stopped.

4. A process for the production of unsaturated hydrocarbons selected from the group consisting of ethylene, propylene and acetylene by thermal cracking of hydrocarbons which are liquid under normal conditions in hot gas at temperatures of from 600 to 1400" C. and pressures of 2 to 50 excess atmospheres, which comprises introducing a liquid hydrocarbon onto the inner wall of a cylindrical reaction zone spreading out said liquid hydrocarbon to be cracked to a film-like rotating band on said inner wall of said cylindrical Zone by means of steam introduced tangentially with respect to said inner wall at a temperature of 200 to 400 C. and at a speed of from to 200 meters per second, and vaporizing and cracking the liquid hydrocarbons by means of hot gases at 800 to 1500 C. produced in a burner arranged in front of said cylindrical zone and flowing through said cylindrical zone in axial direction.

5. A process as claimed in claim 4 wherein the hot gaseous cracking product is rapidly cooled by partial decompression of the reaction gas.

References Cited in the file of this patent UNITED STATES PATENTS 2,372,591 Lonngren Mar. 27, 1945 2,413,407 Dreyfuss Dec. 31, 1946 2,750,420 Hepp June 12, 1956 2,750,434 Krejci June 12, 1956 

1. A PROCESS FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF ETHYLENE, PROPYLENE AND ACETYLENE BY THERMAL CRACKING OF HYDROCARBONS WHICH ARE LIQUID UNDER NORMAL CONDITIONS IN HOT GASES AT TEMPERATURES OF ABOUT 600 TO 1400* C., WHICH COMPRISES INTRODUCING A LIQUID HYDROCARBON ONTO THE INNER WALL OF A CYLINDRICAL REACTION ZONE, SPREADING OUT SAID LIQUID TO BE CRACKED TO A FILM-LIKE ROTATING BAND ON SAID INNER WALL OF SAID CYLINDRICAL CHAMBER BY MEANS OF STEAM INTRODUCED TANGENTIALLY WITH RESPECT TO SAID INNER WALL AND HAVING A TEMPERATURE BELOW THAT WHICH EFFECTS APPRECIABLE CRACKING AND AT A SPEED OF 50 TO 300 METERS PER SECOND, AND VAPORIZING AND CRACKING THE LIQUID HYDROCARBONS BY MEANS OF A HOT GAS WHICH IS MADE TO ENTER THE CYLINDRICAL ZONE AT A TEMPERATURE OF FROM 800 TO 1500* C. AND WHICH FLOWS THROUGH SAID CYLINDERICAL ZONE IN AXIAL DIRECTION. 